1. Field Of The Invention
This invention relates to a tandem master cylinder, primarily for a vehicle hydraulic braking system, having a housing containing two pressure chambers for connection, in use, to separate braking circuits, and pressure piston means movable in the housing under the influence of a single force input device in order to supply fluid under pressure from the chambers to the circuits.
2. Description Of The Prior Art
When such a master cylinder is to be used in a vehicle such as an agricultural tractor for example, in which wheels at opposite sides of the vehicle are required to be braked simultaneously for normal retardation, or individually for steering purposes, it is necessary to provide for pressure fluid transfer between the chambers during simultaneous operation of the brakes in order to compensate for unequal brake wear, and to interrupt the transfer when the brakes are operated individually. One form of conventional arrangement of this kind is described in the earlier British Pat. No. 2074272 in which a selector valve assembly is used in conjunction with a tandem master cylinder in order to provide the required normal retardation and steering assistance modes of operation. Although this operates satisfactorily, it is complicated and expensive to produce and requires considerable installation space. Moreover, it is not readily susceptible to the incorporation of power servo means which is often a requirement on modern vehicles.